Linear actuators have been heretofore provided and are commercially available in which two sets of rollers, each set around the central drive shaft and skewed with respect to the axis of the shaft so that as the shaft rotates the rollers contact the shaft and relatively move the shaft and rollers axially. The rider assembly thus advances along the shaft as the shaft rotates. The rollers are held in contact with the shaft by spring pressure that urges the two halves of the actuator or rider toward each other such as in U.S. Pat. No. 3,272,021. This device has several features including low cost pitch selection by simply changing the roller skew angle and automatic load protection by setting the closing spring load. After a period of time, however, it causes jamming due to bearing failure and does not solve the problem of remote disengagement nor provide means for passing over bearings supporting a long shaft. At other times the linear actuator has been provided in which a block was partly severed leaving a hinge to act between the two severed parts of the block with means to expand the two parts of the block for release of rolls carried by the block such as in U.S. Pat. No. 3,425,284. This arrangement is costly to manufacture and keep in repair.